Restenosis
Stenosis is the narrowing of the blood vessel lumen. In the case of the heart, stenosis of cardiac circulation can lead to acute infarction with subsequent ischemia. Stenosis is frequently treated with angioplasty. Neointimal formation after stent implantation can cause luminal narrowing called restenosis. Restenosis is induced by initial platelet adhesion and thrombus formation followed by immunocytic adhesion on the stent surface and injured vessel wall. The thrombus then releases factors that activate the proliferation of smooth muscle cells.
While percutaneous transluminal angioplasty (PTA), a method of expanding a blood vessel blocked by plaque, presently enjoys wide use, it suffers from two major problems. First, the blood vessel may suffer acute occlusion immediately after or within the initial hours after the dilation procedure. The second major problem encountered in PTA is the re-narrowing of an artery after an initially successful angioplasty. This re-narrowing is referred to as “restenosis” and typically occurs within the first six months after angioplasty. Restenosis is believed to arise through the proliferation and migration of smooth muscle cells arterial wall, as well as through geometric changes in the arterial wall referred to as “remodeling.” It has similarly been postulated that the delivery of appropriate agents directly into the arterial wall could interrupt the cellular and/or remodeling events leading to restenosis. However, the results of attempts to prevent restenosis in this manner have been mixed.
A device such as an intravascular stent can be a useful adjunct to PTA, particularly in the case of either acute or threatened closure after angioplasty. The stent is placed in the dilated segment of the artery to mechanically prevent abrupt closure and restenosis. Unfortunately, even when the implantation of the stent is accompanied by aggressive and precise antiplatelet and anticoagulation therapy (typically by systemic administration), the incidence of thrombotic vessel closure or other thrombotic complication remains significant, and the prevention of restenosis is not as successful as desired. An undesirable side effect of the systemic antiplatelet and anticoagulation therapy is an increased incidence of bleeding complications, limiting its use. A suitable device would work locally to deliver a therapeutic agent that would prevent thrombus formation and inhibit smooth muscle cell proliferation without undesirable side-effects.
Stents
Recent major breakthroughs have made new materials available for percutaneous peripheral arterial and coronary artery intervention procedures. Typically, a stent is an inserted mesh of wires that stretch and mold to the arterial wall to prevent reocclusion. The arterial and coronary artery stents have made progressive structural improvements leading to the evolution of third generation stents or coated stents. Stents are described for instance in U.S. Pat. Nos. 6,235,053; 6,165,209; 6,129,725; 6,241,760; and 6,197,047.
Implantable medical devices capable of delivering medicinal agents have been described. Several patents are directed to devices utilizing biodegradable or bioresorbable polymers as drug containing and releasing coatings, including U.S. Pat. Nos. 4,916,193; 4,994,071; and 6,096,070. Other patents are directed to the formation of a drug containing hydrogel on the surface of an implantable medical device, these include U.S. Pat. Nos. 5,221,698; and 5,304,121. Still other patents describe methods for preparing coated intravascular stents. U.S. Pat. No. 5,464,650 describes coating stents via application of polymer solutions containing dispersed therapeutic material to the stent surface followed by evaporation of the solvent. U.S. Pat. No. 6,099,561 describes stents with ceramic-like coatings. U.S. Pat. No. 6,231,600 describes stents with hybrid coatings including a time released restenosis inhibiting coating and a non-thrombogenic coating to prevent clotting on the device. U.S. Pat. No. 6,214,901 describes a biocompatible polymer suitable for coating implantable medical devices and delivering therapeutics suspended therein. Additional coatings for medical devices are described for instance in U.S. Pat. Nos. 6,071,305; 6,179,817; and 6,218,016.
Several therapeutic agents have been proposed for treating or preventing restenosis. U.S. Pat. No. 6,214,868 describes preventing or treating coronary restenosis which comprises administering an effective amount of a catechin, derived from a green tea extract. US Patent No. describes inhibiting restenosis with a peptide abundant in basic amino acid residues linked via its C-terminus to a peptide of at least two consecutive hydrophobic amino acid residues. U.S. Pat. No. 6,239,118 describes inhibiting restenosis with a substituted adenine derivative such as 2-chloro-deoxyadenisine. U.S. Pat. No. 6,171,609 describes inhibiting restenosis with an inhibitor of vascular smooth muscle cell contraction. U.S. Pat. No. 6,241,718 describes inhibiting restenosis by applying cryogenic energy to a treatment site. U.S. Pat. No. 6,156,350 describes inhibiting restenosis by flushing with a solution with a pH below 4.0 such as a hydrochloric acid.
Pulmonary Hypertension
Pulmonary hypertension has been an enigma to the medical profession both diagnostically and therapeutically. Its well known “mirror image cousin,” arterial hypertension is probably the most diagnosed and treated medical condition, while this poor relation remains undiagnosed, untreated and quietly deadly. Unlike arterial hypertension, pulmonary hypertension can not be readily diagnosed such as by a sphygmomanometer.
Pulmonary hypertension is defined when the pressure in the pulmonary artery exceeds 25 mm of mercury at rest or 30 mm of mercury during exercise. There are two forms of pulmonary hypertension. One is known as primary pulmonary hypertension where the cause is unknown and second form is referred to as secondary pulmonary hyertension, meaning that it is secondary to another identifiable underlying cause.
Pulmonary hypertension usually occurs in young adults, with a mean age of 45, varying from 15 to 66 years of age. Approximately 62% are female. The median survival time after diagnosis is approximately 2.5 years. Secondary pulmonary hypertension can result from a multitude of diseases including cardiac problems such as sever mitral stenosis, severe aortic stenosis, left to right shunts (VSD), congestive heart failure, diastolic dysfunction, to list a few of the cardiac causes. Other causes are obstructive sleep apnea, chronic pulmonary emboli, pulmonary parenchymal disease such as emphysema, pulmonary fibrosis or chest wall deformities. It also occurs in connective tissue disease e.g. lupus erythematosus, polymiositis, rheumatoid arthritis, scleroderma and with the CREST syndrome. Secondary pulmonary hypertension has been associated with portal hypotension, and with the use of appetite suppressants.
Elevated pulmonary artery pressure has been found to be a specifically significant prognostic factor in chronic obstructive pulmonary disease patients receiving long term oxygen therapy. In a recent study at the University Hospital in Strasbourg France, Oswald-Mammosser and co-workers found that the five year survival in patient's with severe COPD with normal resting pulmonary artery pressure was 62% and in patients with elevated pulmonary artery pressure the survival was only 36%. The means of treatment for primary or secondary pulmonary hypertension are medical or surgical. At present, most of the medical treatments are experiment and are primarily related to prostacyclin analogues given either orally, inhaled or by infusion. There have also been several studies with inhaled nitrate oxide and oral endothelin receptor antagonists. None of these produced any dramatic results. WO 01/34088 discusses the use of vasoactive intestinal peptide (VIP) for treatment of pulmonary hypertension.
Surgery for treatment of pulmonary hypertension usually consists of lung transplantation, single, bilateral or heart with bilateral lung. Most patients have a waiting period of two to three years for an appropriate donor, obviating the need for many patients who succumb to pulmonary hypertension within that time. Survival at five years post-transplantation is 37-44%. At present it does not appear to be a viable treatment. The lung volume reduction procedure remains a questionable option for COPD.
Cancer
In spite of numerous advances in medical research, cancer remains the second leading cause of death in the United States. In the industrialized nations, roughly one in five persons will die of cancer. Traditional modes of clinical care, such as surgical resection, radiotherapy and chemotherapy, have a significant failure rate, especially for solid tumors. Failure occurs either because the initial tumor is unresponsive, or because of recurrence due to regrowth at the original site and/or metastases. Even in cancers such as breast cancer where the mortality rate has decreased, successful intervention relies on early detection of the cancerous cells. The etiology, diagnosis and ablation of cancer remain a central focus for medical research and development.
Neoplasia resulting in benign tumors can usually be completely cured by removing the mass surgically. If a tumor becomes malignant, as manifested by invasion of surrounding tissue, it becomes much more difficult to eradicate. Once a malignant tumor metastasizes, it is much less likely to be eradicated.
The three major cancers, in terms of morbidity and mortality, are colon, breast and lung. New surgical procedures offer an increased survival rate for colon cancer. Improved screening methods increase the detection of breast cancer, allowing earlier, less aggressive therapy. Numerous studies have shown that early detection increases survival and treatment options. Lung cancer remains largely refractory to treatment.
Excluding basal cell carcinoma, there are over one million new cases of cancer per year in the United States alone, and cancer accounts for over one half million deaths per year in this country. In the world as a whole, the five most common cancers are those of lung, stomach, breast, colon/rectum, and uterine cervix, and the total number of new cases per year is over 6 million. Only about half the number of people who develop cancer die of it.
Vasodilators
Vasodilators cause vasodilation of or in increased rate of blood flow through the arteries. Thus, upon administration of VIP and/or NP, vasodilation or rate of blood flow would be expected to increase.
Vasoactive Intestinal Peptide
VIP is a basic, linear 28 amino acid polypeptide isolated initially form porcine duodenum (Mutt et al. (1974) Eur. J. Biochem. 42:581-589) and widely found in the central and peripheral nervous systems and digestive tract. VIP has strong vasodilating properties and hypotensive activity and systemic vasodilatory activity. Administered intravenously (IV) or directly into the heart, VIP increases heart rate and contractile force. Anderson et al. (1988) J. Cardio. Pharmacol. 12:365-371; Rigel et al. (1988) Am. J. Physiol. 255:H317-319; Karasawa et al. (1990) Eur. J. Pharmacol. 187:9-17; and Unverferth et al. (1985) J. Laboratory. Clin. Med. 106:542-550.
The amino acid structure of VIP was clarified in 1974, and since this structure is similar to both secretin and glucagons, VIP is considered to be a peptide hormone belonging to the glucagons-secretin family. Other members of this family of structurally related peptides include gastric inhibitory peptide (GIP), growth hormone releasing factor (GHRF) and adenylate cyclase-activating peptide (PACAP). Like all secretory peptides, VIP is derived by proteolytic cleavage from a larger precursor molecule. The 170 amino acid precursor preproVIP contains histidine isoleucine, another biologically active peptide. Itoh et al. (1983) Nature 304:547-549. VIP contains at least two functional regions: a region of receptor-specific binding and a region involved in biological activity. Gozes et al. (1989) Mol. Neurobiol. 3:201-236.
VIP mediates or modulates several basic cell functions. These include brain activity, endocrine functions, cardiac activity, respiration, digestion and sexual potency. The widespread physiologic distribution of VIP correlates with its involvement in a broad spectrum of biological activities. The actions of VIP are of a complex nature, encompassing receptor modulation, inducting release of neurotrophic factors, neurotransmission and neuromodulation. VIP occurs widely in the central and peripheral nervous systems and digestive tract, and may play a role in parasympathetic responses in the trachea and gastrointestinal tract.
VIP is an important modulator of cell growth, differentiation and survival during development of the sympathetic nervous system. VIP acts as a neuromodulator in several responses. Ferron et al. (1985) Proc. Natl. Acad. Sci. USA 82:8810-8812; and Kawatani et al. (1985) Science 229:879-881. In cholinergic studies VIP has a selective effect on muscarinic excitation in sympathetic ganglia with no apparent effect on nicotinic responses, indicating that VIP has intrinsic properties affecting electrical activity and also interacts with other neurotransmitter systems to modulate physiologic responses.
VIP has been found in glial cells and appears to be of physiological importance. VIP mediates communication between neurons and glia, a relationship of fundamental importance to neurodevelopment and function.
VIP immunoreactive fibers are present in and appear to be intrinsic to the canine heart. Weihe et al. (1981) Neurosci. Let. 26:283-288; and Weihe et al. (1984) Cell Tiss. Res. 236:527-540. VIP-containing neurons are present in canine hearts where VIP exerts a strong global myocardial effect similar to, but more sustained than, the adrenergic effect. The effect is qualitatively similar to other inotropic drugs that act through specific cell surface membrane receptors coupled to adenylate cyclase, for example β-adrenergic agonists such as proterenol.
VIP receptors are found in both canine and human hearts, thus canines are an appropriate model for VIP in humans. Vagal, efferent stimulation of β-blocked, atropinized dogs increased heart rate and contractile force, an effect that may be due to the release of VIP. Rigel et al. (1984) Am. J. Physiol. 246 (heart circ. physiol. 15) H168-173. VIP is released from dog atria when parasympathetic nerves are stimulated. Hill et al. (1993) J. Auton. Nerv. Sys. 43:117-122; and Hill et al. (1995).
Many different potential therapeutic uses of VIP, VIP analogues and VIP-like polypeptides have been proposed. Due to the widespread distribution and variety of activities of VIP, VIP analogues and VIP-like peptides have been proposed as treatment for various conditions including, among others, asthma and erectile dysfunction.
VIP is active when present in amounts of only picograms, and is stable in solution. This makes it particularly suited for use in a medicinal context.
VIP has inotropic and chronotropic effects due to its vasodilatory properties. VIP acts as a bronchodilator and a relaxant of pulmonary vascular smooth muscle. The inotropic state of the ventricle may be affected by the activation of several receptors, some of which are coupled to adenylate cyclase. Foremost among these is the β-adrenergic receptor, which, when activated by its corresponding neurotransmitter norepinephrine, mediates increased cardiac contractility.
Additional positive inotropic cardiac receptor pathways have been identified although physiologic roles have not yet been established. These include pathways that respond to β-adrenergic agonists including histamine, serotonin, enkephalins and VIP. Of these, VIP is a potentially important agonist because it is present in nerve fibers in the heart, is coupled to adenylate cyclase, and, when administered IV, mediates both increased contractility and coronary vasodilation. There is some evidence that VIP has two discrete binding sites specific to the central nervous system.
The time-course of chronotropic effects of VIP is dose-dependent; however the time-course for recovery from inotropic effects is not. This may be due to variation in neurotransmitter levels in extracellular spaces, occurring due to heart movement. At a constant level of sympathetic nerve stimulation, dogs whose hearts were paced at different rates showed different recovery times from the inotropic response. Thus the recovery from VIP inotropic effects is affected by heart rate, which in turn is altered by the chronotropic effects. The inotropic and chronotropic effects of VIP are therefore related but do not occur through the same mechanism. There may be different receptors for the two responses or the biochemical cascade initiated differs for the two.
Intact endothelium is necessary to achieve vascular relaxation in response to acetylcholine. The endothelial layer modulates autonomic and hormonal effects on the contractility of blood vessels. In response to vasoactive stimuli, endothelial cells release short-lived vasodilators called endothelium-derived relaxing factor (EDRF) or endothelium-derived contracting factor. Endothelial cell-dependent mechanisms are important in a variety of vascular beds, including the coronary circulation.
The natural properties of VIP have been improved. The C-terminus holds a receptor recognition site, and the N-terminus holds the activation site with minimal binding capacity. These are essential to VIP function. Peptides non-essential to function have been manipulated and altered, resulting in some cases in increased levels of activity over natural VIP. These VIP analogues and VIP-like peptides can be utilized in any situation where VIP is effective. Some VIP analogues have improved storage properties and increased duration of action, and therefore may be superior drugs. EP A 0613904; and U.S. Pat. Nos. 4,737,487; 5,428,015; and 5,521,157. VIP antagonists alter VIP function. U.S. Pat. No. 5,217,953.
VIP inervation has been demonstrated in the airways and pulmonary vessels (Dey et al. (1981) Cell Tiss. Res. 220:231-238), and the lungs are believed to be an important physiological target for VIP. The rat and guinea pig brains have VIP-specific receptor sites. Taylor et al. (1979) Proc. Natl. Acad. Sci. USA 76:660-664; Robberecht et al. (1978) Eur. J. Biochem. 90:147-154. The receptor-molecule complex has been identified in the intestine and lung. Laburthe et al. (1984) Eur. J. Biochem. 139:181-187; and Paul et al. (1985) Regul. Peptide 3:S52. Two classes of receptors with different pharmacological properties have been detected in rat lung and in human colonic adenocarcinoma cells. Atthi et al. (1988) J. Biol. Chem. 263:363-369; and El Baatari et al. (1988) J. Biol. Chem. 263:685-689.
cDNAs encoding rat and human VIP receptors have been cloned; at least one of these receptors is structurally related to the secretin receptor; at least one of these receptors is structurally related to the secretin receptor. Ishihara et al. (1992) Neuron; Sreedharan et al. (1993) Biochem. Biophys. Res. Comm. 193:546-553; and Sreedharan et al. (1995) Proc. Natl. Acad. Sci. USA 92:2939-2943. mRNA for this VIP has been found in several tissues including liver, lung, intestine and brain. mRNA for another VIP receptor has been found in stomach, testes and brain.
The VIP receptor or receptors may be coupled to adenylate cyclase, as a VIP-stimulated adenylate cyclase has been identified in various areas of the central nervous system as well as the liver and pituitary. Quick et al. (1978) Biochem. Pharmacol. 27:2209-2213; Deschodt-Lanckman et al. (1977) FEBS Lett. 83:76-80; and Rostene (1984) Progr. Neurobiol. 22:103-129. Studies of rat sensory neurons show that VIP transcription may be increased via activation of cellular transcription factors that bind to a cyclic adenosine monophosphate (cAMP) responsive element. Dobson et al. (1994) Neurosci. Lett. 167:19-23; Tsukada et al. (1987) J. Biol. Chem. 262:8743-8787; and Giladi et al. (1990) Brain Res. Mol. 7:261-267.
VIP action on cAMP may be mediated via G-proteins, signal transducers that stimulate hydrolysis of GTP to GDP, as GTP and its analogues inhibit VIP-receptor binding and potentiate cAMP synthesis in response to VIP. Paul (1989) Biochem. Pharmacol. 38:699-702. If the VIP-receptor is coupled to G-proteins, this could explain the array of VIP effects found, as G-proteins are widespread and involved in several signal transduction pathways. VIP induces its own mRNA in PC12 cells, probably as a result of its activation of adenylate cyclase. Tsukada et al. (1995) Mol. Cell. Endocrinol. 107:231-239. Regulation of VIP expression occurs also at a translational or post-translational level. Agoston et al. (1992). VIP may act as an autocrine regulator of its own synthesis.
VIP treatment produces a loss of responsiveness to subsequent rechallenges; a short-term exposure to VIP results in internalization of the receptor-peptide complex, a feature that may be tissue-specific. Rosselin et al. (1988) Ann. NY Acad. Sci. 527:220-237; Boissard et al. (1986) Cancer Res. 46:4406-4413; and Anteunis et al. (1989) Am. J. Physiol. 256:G689-697. After internalization, VIP is degraded in lysosymes and may serve as an intracellular effector, while the receptors are recycled to the cell surface.
VIP binding sites and VIP-stimulated adenylate cyclase can be reduced by preincubation with different agents, although the different agents appear to function by different mechanisms. Turner et al. (1988) J. Pharmacol. Exp. Ther. 247:417-423. The VIP receptor appears to be translocated to a light vesicle fraction after such exposure. In some cell lines, the half-life of the receptor was around 2 days, and N-glycosylation was necessary for translocation. An internalized VIP receptor is dissociated from adenylate cyclase activity, although the internalization process is not completely independent of cAMP accumulation. Hejblum et al. (1988) Cancer Res. 48:6201-6210. VIP signal transduction thus relies on multiple pathways other than elevation of cAMP.
Neuropeptide
Neuropeptide Y (NPY) is a 36-amino acid peptide neurotransmitter that is located throughout the central and peripheral nervous systems. Tatemoto (1982) Proc. Natl. Acad. Sci. USA 79:5485; and Hazlewood (1993) Proc. Soc. Exp. Biol. Med. 202:44. It affects a broad range of phenomena, including blood pressure regulation, memory, anxiolysis/sedation, food and water appetite, vascular and other smooth muscle activity, intestinal electrolyte secretion, and urinary sodium excretion. Colmers and Wahlestedt, The Biology of Neuropeptide Y and Related Peptides (Humana Press, Totowa, N.J. 1993).
Peptide YY (PYY) is also a 36 amino acid peptide and has significant sequence homology (70%) to NPY. Tatemoto et al. (1982) Nature 296:659. Its anatomical distribution is similar to that of NPY, although it is located mainly in the endocrine cells of the lower gastrointestinal tract. Bottcher et al. (1984) Regul. Pept. 8:261 (1984). Like NPY, PYY stimulates feeding in rats. Morley et al. (1985) Brain Res. 341:200. Along with the pancreatic polypeptide (PP), NPY and PYY have a common tertiary structure, characterized by the so-called PP-fold. Glover (1985) Eur. J. Biochem. 142:379. Both NPY and PYY show about a 50% sequence homology with PP.
Because of their structural similarities, NPY and PYY have a number of common receptors. At least four receptor subtypes, Y1, Y2, Y3, and Y4/PP, have been identified. The affinity for NPY, PYY, and various fragments thereof varies among the subtypes. WO 95/17906. As used herein, NP encompasses all forms of neuropeptides with stenosis-inhibiting activity.